Tie::Hash(3)

NAME
Tie::Hash, Tie::StdHash - base class definitions for tied hashes

SYNOPSIS
    package NewHash;
    require Tie::Hash;
    @ISA = (Tie::Hash);
    sub DELETE { ... }          # Provides needed method
    sub CLEAR { ... }           # Overrides inherited method
    package NewStdHash;
    require Tie::Hash;
    @ISA = (Tie::StdHash);
    # All methods provided by default, define only those needing overrides
    sub DELETE { ... }
    package main;
    tie %new_hash, 'NewHash';
    tie %new_std_hash, 'NewStdHash';

DESCRIPTION
This module provides some skeletal methods for hash-tying classes. See the perltie manpage for a list of the functions required in order to tie a hash to a package. The basic Tie::Hash package provides a "new" method, as well as methods "TIEHASH", "EXISTS" and "CLEAR". The Tie::StdHash package provides most methods required for hashes in the perltie manpage. It inherits from Tie::Hash, and causes tied hashes to behave exactly like standard hashes, allowing for selective overloading of methods. The "new" method is provided as grandfathering in the case a class forgets to include a "TIEHASH" method.

For developers wishing to write their own tied hashes, the required methods are briefly defined below. See the the perltie manpage section for more detailed descriptive, as well as example code:

TIEHASH classname, LIST
    The method invoked by the command "tie %hash, classname". Associates a new hash instance with the specified class. "LIST" would represent additional arguments (along the lines of the AnyDBM_File manpage and compatriots) needed to complete the association.

STORE this, key, value
    Store datum value into key for the tied hash this.

FETCH this, key
    Retrieve the datum in key for the tied hash this.

FIRSTKEY this
    Return the (key, value) pair for the first key in the hash.

NEXTKEY this, lastkey
    Return the next key for the hash.

EXISTS this, key
    Verify that key exists with the tied hash this.

    The Tie::Hash implementation is a stub that simply croaks.

DELETE this, key
    Delete the key key from the tied hash this.

CLEAR this
    Clear all values from the tied hash this.

CAVEATS
The the perltie manpage documentation includes a method called "DESTROY" as a necessary method for tied hashes. Neither Tie::Hash nor Tie::StdHash define a default for this method. This is a standard for class packages, but may be omitted in favor of a simple default.

MORE INFORMATION
The packages relating to various DBM-related implementations (DB_File, NDBM_File, etc.) show examples of general tied hashes, as does the the Config manpage module. While these do not utilize Tie::Hash, they serve as good working examples.